1. Field of the Invention
The present invention relates generally to electrical signal injecting apparatus for use with an underwater cable. More specifically, the present invention relates to a portable water tight signal injecting apparatus for inducing a 1024 Hz signal into an underwater cable which allows the user to track the signal with a tracking probe tuned to the same frequency.
2. Description of the Prior Art
Underwater cables are needed for communications, transmission of video and audio data and the like. It has become common practice to bury these cables in sand or under the ocean floor to avoid damage. When a cable breaks or is damaged there will be requirement to locate the cable to effect repairs to the cable or replacement of the cable.
Accordingly, there is a need to have an apparatus for locating an underwater cable which is buried in sand or under the ocean floor.
The present invention overcomes some of the difficulties of the prior art including those mentioned above in that it comprises a relatively simple yet highly effective pulse width modulated cable signal injecting apparatus designed to function in an underwater environment. The signal injecting apparatus induces a 1024 hertz tracking signal into a subsea cable allowing an operator to track the signal with a tracking probe tuned to the same frequency.
A microcontroller generates a continuous 1024 hertz square wave signal which is supplied through a NAND gate to a field effect transistor. When the field effect transistor is switch on a tank circuit comprising a pair of capacitors and the primary of an signal injector coil starts oscillating and will continue to oscillate when the field effect transistor is switch off.
The power level for the signal to the cable is determined by an operator based on the operator inputs from depressing a pair of push button switches, which are the power up/down push button switches. The microcontroller, responsive to the operator inputs from the push button switches, outputs a digital word to a digital-to-analog converter that represents the required power level. The analog output signal from the digital-to-analog converter is supplied to a control loop circuit which adjust the power level by enabling and disabling the NAND gate. When the NAND gate is enabled, the 1024 HZ signal passes through the NAND gate turning on the field effect transistor and thus causing the primary of a signal injector coil to start oscillating. When the signal injecting coil""s current level reaches a point at which the voltage at the positive input of a comparator reaches a threshold voltage at the negative input of the comparator, the output of the comparator will switch from a low to a high which in combination with a Flip-Flop disables the NAND gate turning off the field effect transistor.